There are a number of personal security locks on the market or known to the prior art. Some of these locks require a key and are thus continuously subject to the hazard of loss of the key. Other such locks are quite complicated. One form of lock has a flat shank portion of rather thin weak metal with a right-angle hook end to engage the striker plate and a spring-clamp to engage toothed edges along the shank. This construction is not strong enough to resist an intruder. Also this type of lock can be dislodged by use of a long thin-nosed pliers, available to burglars, which can be used to squeeze the spring-clamp to the open position.
Another form of door lock is shown in U.S. Pat. No. 3,352,587 by R. M. HARVEY using a hook member with a series of bore holes therealong into which a pin is engaged. The pin in turn is engageable with a pair of blocks, one at each end. The holes in the blocks are off-center so that the blocks can be rotated into abutting positions against the frame and door. This is a four-piece arrangement. Rattling the door can work the blocks off the pins and allow the lock to open.